Displacement sensor for contactless measurement of a relative position, production method for a magnetic field sensor arrangement and magnetic field sensor

This application is a continuation of PCT International Application No. PCT/EP2017/074266, filed on Sep. 25, 2017, which claims priority under 35 U.S.C. § 119 to German Patent Application No. 102016218530.6, filed on Sep. 27, 2016.

The present invention relates to a displacement sensor and, more particularly, to a displacement sensor for contactless measurement of a relative position of a magnetic field source.

Linear movements are measured, for example, to control machine tools in pneumatics, in automation technology and robotics, as well as in the automotive sector. A contactless detection of movements has the advantage, inter alia, of being wear-free. Optical and magnetic contactless measuring methods are the most common of the contactless measuring methods. While the optical methods guarantee a very high level of accuracy by virtue of the small wavelength of the light, magnetic methods are far less sensitive to contamination and damage, in particular due to the fact that magnets and sensor components can be fully encapsulated in a non-magnetic hermetic protective material.

Various manufacturers offer displacement sensor systems in which the position of a displaceable permanent magnet is determined, for example, with the help of a two-dimensional or three-dimensional Hall-effect sensor. In this case, to detect the linear relative movements at a location, two magnetic field components which are perpendicular to each other are measured and their quotient is evaluated for position identification. This approach has the advantage that, in areas in which one field component assumes an extreme value and thus does not detect small displacements, the other field components respond all the more strongly such that equally high measuring accuracy is approximately high throughout the entire measuring range. Further, this principle is comparatively less sensitive to a variation of the absolute magnetic field strength, since relative values between the field components are used for position detection.

shows an arrangement in which, for contactlessly detecting a linear movement, a magnetic field sensor, in particular a Hall-effect sensor, is fixedly assembled, for example on a housing wall, and detects the magnetic field of a movable permanent magnet. Corresponding to the north/south polarization along the movement direction of the permanent magnet, the component of the magnetic field which runs in the movement direction is designated magnetic field component Bz, and the component which runs transversely thereto is designated By. The entire measuring range in the z direction which is covered by the Hall-effect sensoris indicated by the reference number.

shows the curve of the components By and Bz of the magnetic flux density as a function of the location z of the permanent magnet. The zero position is the position in which the permanent magnetand the sensorare directly opposite each other.

The angle α, which can be calculated according to the following equation (1), is used as a measuring signal.

The curve of the quantity |{right arrow over (B)}| of the magnetic flux density is shown inas a function of the location z. The vector quantity |{right arrow over (B)}| of the magnetic flux density is calculated in a known manner from the individual components By and Bz according to the following equation (2). Corresponding calculation rules apply, as known to a person skilled in the art, when using other coordinate systems and also when adding a third magnetic field component Bx.||=√{square root over ()}  (Eqn. 2)

As shown in, the angle α depends, up to a certain value comparatively linearly, on the position of the permanent magnetwith respect to the Hall-effect sensor. The currently measured characteristic is usually further linearized, as shown inby the curve α_lin. This linearized curve α_lin then forms the output characteristic of the sensor.shows the curve of the position signal OUT which is output by the sensor.

Most commercially available 3D Hall-effect sensors can only be operated in the presence of a sufficiently strong magnetic field. If the permanent magnet is located outside the range of detection of the sensor, a sensor signal is no longer obtainable. German patent DE 10 2012 205 903 B4 proposes that the magnetic field sensor which detects the position of the magnetic field source should have a plurality of magnetic field probes. Each of the magnetic field probes outputs a position signal, and this position signal is based on at least two spatial components of the magnetic flux density of the magnetic field. An external control and calculating unit is provided, which outputs a total output signal of the displacement sensor based on the plurality of position signals. Furthermore, a storage unit is provided which stores the individual position signals. The control and calculating unit decides, based on a calculated value of the magnetic flux density, which is measured at the location of the respective magnetic field probe, if a current position signal is to be output as the position signal, or if the previously stored position signal is to be output and the further calculation to be taken as a basis.

For some applications, the provision of a separate control and calculating unit is, however, not practical since the overall displacement sensor would become too cumbersome and prone to faults.

A displacement sensor comprises a magnetic field source generating a magnetic field and a magnetic field sensor arrangement adapted to contactlessly detect a relative position of the magnetic field source with respect to the magnetic field sensor arrangement. The magnetic field sensor arrangement includes a first magnetic field sensor adapted to generate a first position signal and a second magnetic field sensor adapted to generate a second position signal. Each of the first magnetic field sensor and the second magnetic field sensor has a magnetic field probe adapted to detect a magnetic flux density of the magnetic field, an evaluation unit for evaluating an output signal of the magnetic field probe, and a communication interface for emitting and receiving a plurality of communication signals. The first magnetic field sensor and the second magnetic field sensor are connected to each other via a data bus for transmitting the communication signals.

The present invention will now be explained in greater detail using the exemplary embodiments depicted in the following figures. Identical parts are here provided with identical reference numbers and identical component names. Furthermore, individual features or combinations of features from the shown and described embodiments taken separately represent independent inventive solutions or solutions according to the invention.

In general principle, a displacement sensor arrangement according to the present invention functions as explained with respect to; a magnetic field sensor is fixedly assembled, while a permanent magnetis mounted to be movable linearly (or along a curved path) with respect to the magnetic field sensor. The permanent magnetis polarized for example such that its north/south axis is oriented parallel to the movement direction. The principles of the present invention are generally also applicable to arrangements in which the permanent magnetis polarized such that its north/south axis runs transversely to the movement direction. The permanent magnetcan be displaced from the zero position shown inin two directions by a travel distancedefined by the respective application. The principles according to the invention can also be applied to other magnetic field sources, for example, electromagnets, and to magnetic field sensors such as magnetoresistive sensors or inductive sensors.

In the present description, on the one hand the values of the magnetic field in the movement direction Bz, and on the other hand the values of the magnetic field transversely to the movement direction By are used as magnetic field components measured in dependence on the position of the permanent magnetOf course, the Bx values which run orthogonally to By can also be used for the calculation.

A compact and autonomous magnetic field sensor arrangementaccording to an embodiment of the invention shown inis able to cover an extended measuring range. The sensor arrangementincludes a first magnetic field sensorconfigured as master (hereinafter designated simply as “master”) and one or more second magnetic field sensorsconfigured as slaves (hereinafter designated simply as “slave”) to be connected to each other via a data bus. If a plurality of second magnetic field sensors-to-N are provided, these can be connected to each other in series, as shown in. According to an exemplary embodiment, seven magnetic field sensors-to-configured as slaves are thus connected to each other in a cascade, wherein a signal path is provided both from the masterto the slavesand from the slavesto the master.

As shown in, the magnetic field sensors,are connected to each other directly via a leadframe which forms individual linesof the data bus. The plurality of second magnetic field sensorsare arranged in series along a displacement path of the magnetic field source. The displacement sensor according to the invention including the permanent magnetand the sensor arrangementcan thus be adapted in a flexible manner to a great variety of spatial conditions. Not only linear movements can be detected over relatively long, straight distances, but also rotation movements wherein the magnetic field sensorsare arranged along a radius around the rotation axis of a moving part. Therefore, a PCB is no longer required and the magnetic field sensor arrangementis particularly robust and can be extensively miniaturized. With each individual magnetic field sensor,, a measuring range of approximately 30 mm can be covered. By cascading a plurality of individual sensors, a correspondingly greater detectable measuring range can be achieved. For example, in an embodiment, when using a first magnetic field sensorand seven second magnetic field sensors-to-, a maximum measuring range of approximately 240 mm can be covered.

As shown in, the magnetic field sensor arrangementhas an input/output interfacewhich links the magnetic field sensor arrangementto external components. As shown in, the input/output interfaceserves, on the one hand, to connect the magnetic field sensor arrangementto groundand an external power supplyand, on the other hand, to output an output signal which reflects the position of the magnet. The output signal here, as is also usual in the case of conventional displacement sensors, can be either an analog signal, a pulse width modulation (PWM) signal or a binary coded signal (according to the SENT protocol, for example). Power is supplied for example by a direct current voltage of 4 V to 16 V. It is clear to the person skilled in the art that, in another embodiment, the measurement data can be transmitted to the outside with wireless technology, such as a radio connection. The energy which is required for operation of the magnetic field sensors,can also be supplied contactlessly (for example, by inductive coupling or energy harvesting).

In the embodiment shown in, all magnetic field sensors,are constructed identically. Each magnetic field sensor has a magnetic field probewhich detects the magnetic field and is arranged on an application specific integrated circuit (ASIC). In an embodiment, the magnetic field probeis the transducer element which carries out the physical conversion of the magnetic input variable into an electrical signal. Each magnetic field sensor,includes an evaluation unit for evaluating an output signal of the magnetic field probeand a communication interface for emitting and receiving a plurality of communication signals. The first magnetic field sensorand the second magnetic field sensorare connected to each other via the data busfor transmitting the communication signals The ASIChas further electronic circuits, for example a control unit, a communication unit, memory units, and, where applicable, voltage converters and stabilizing circuits. Discrete components such as capacitorscan also be provided.

In the embodiment of, three connecting linesare provided which form the data bus. The data busis bidirectional. However, the number of connecting linescan of course be adapted to the particular requirements of the bus format and bus protocol such that more or fewer linesare also possible. The magnetic field sensors,are according to the invention connected with each other in series in a cascade such that the data which is transmitted over the busis looped through all bus participants respectively. Nevertheless, by providing lineswhich run correspondingly parallel at the leadframe, a parallel or a combined serial/parallel busconnecting the magnetic field sensors-to-N configured as slaves to each other and to the magnetic field sensorconfigured as master is also achievable. Examples of possible data bus protocols are, as mentioned, the SPI (serial peripheral interface), IC (inter-integrated circuit) or SENT (single edge nibble transmission) protocols. The SENT protocol is defined as unidirectional output protocol; for communicating between the magnetic field sensorconfigured as master and the magnetic field sensor(s)configured as slave, a second bidirectional interface is thus required for the communication.

The magnetic field probecan be based on any conventional physical principle which is suitable for detecting the magnetic field. A Hall-effect sensor or a magnetoresistive (MR) sensor, e.g. an anisotropic magnetoresistive (AMR) sensor, a tunnel magnetoresistive (TMR) or a giant magnetoresistive (GMR) sensor, can for example be employed as a magnetic field probe. In the event that GMR technology is used, there is no need for magnets of rare earths since a high degree of accuracy can already be guaranteed for a standard ferromagnet when using a GMR probe.

The anisotropic magnetoresistive effect (AMR) occurs in ferromagnetic materials, the resistivity of which changes with the angle between the magnetic field direction and the current direction. The change in resistance amounts to a small percentage and is useful even with weak magnetic fields. In the case of the TMR effect (tunnel magnetoresistive) the tunnel resistance changes between two ferromagnetic layers, depending on the angle of the magnetization of the two layers. The giant magnetoresistive effect (GMR) was only discovered in 1988. The electrical resistance of two thin ferromagnetic layers, separated by a thin non-magnetic layer, changes depending on the angle of the magnetization in the two ferromagnetic layers to each other and produces changes in resistance of up to 50%. The electrical resistance is the highest in the case of antiparallel magnetization. The change in resistance is not dependent on the current direction. When several layers with different properties and magnetizations are stacked, the characteristics of GMR sensors are determined by their construction. This enables a targeted adaptation of the characteristics to the requirements for a particular measurement application.

The masterand the slavescan be formed by identical magnetic field sensors. The configuration as masteror slavetakes place automatically according to the invention, in that during a configuration step it is determined whether the respective connecting linesare unconnected or connected. If, for example corresponding to the arrangement infor a magnetic field sensor,, it is determined that the terminals on its left side as seen from above are unconnected terminals, it is established that it is intended to be a master. By contrast, if the terminals located on the left side represent connecting lines, the corresponding magnetic field sensor,is configured as slave. During an automatic addressing routine, the address “0x0” can be assigned to the master. The further magnetic field sensors,then receive the address of the adjacent magnetic field sensor+“0x1”.

The masterincludes a signal processing unit which is able to process the signals of all the magnetic field probes of the array, i.e. the probes in the slavesand its own probe, and generate an output signal therefrom which reflects the position of the permanent magnet. The communication between the masterand the slavestakes place via the communication busconnected to the ICs. The slavesmust have at least one magnetic field probe, a device for analogue to digital conversion, and a digital communication interface for internal communication. The master, along with the magnetic field probe, the device for analogue to digital conversion, and the digital communication interface, also contains a signal processing unit for combining all sensor signals and a robust output driver unit for outputting the calculated output signal to an external control unit. Furthermore, the mastercomprises a device for connecting the magnetic field sensor arrangementto an external power supply unit.

The magnetic field sensor arrangementaccording to the invention needs only the magnetic field sensors,and, in another embodiment, does not require any evaluation units. External devices for overvoltage protection, for signal stabilization, for ensuring the electromagnetic compatibility (EMC) or for protecting against electrostatic discharge (ESD) are not necessary either, since the magnetic field sensors,according to the invention include all the required components.

Although the principles according to the invention can also be implemented using commercial magnetic field sensors (see the embodiments of), the invention proposes the magnetic field sensor,which is particularly suitable for arrangement in an array, as shown in greater detail in.

As shown in, terminalsare provided for connecting to further magnetic field sensors,via the data bus, which terminalscan be welded to a leadframe, for example. Further components, such as capacitorsor resistors, can be integrated in the magnetic field sensor,as required. The magnetic field probeand the further electronic components can be arranged on the same semiconductor module or on separate modules which are connected to each other.

In the embodiment shown in, the input/output interfacecomprises four terminals. A power supply terminalcan be connected to an external power supply unit. A ground terminalenables connection to an external reference potential, and an output terminaloutputs the output signal calculated in the magnetic field sensor,. The output signal can be a pulse width modulated (PWM) signal, for example, in the case of which the duty factor encodes the information to be output via the measured magnetic field. Alternatively, an analogue signal, for example an analogue voltage signal, or a digital signal, for example a signal according to the SENT protocol already mentioned, can also be output. A complementary output terminalsupplies an output signal which is complementary to the output signal (for example, an inverted output signal). In the array shown in, the terminalsorwhich are not required in each case remain unconnected.

A displacement sensor according to another embodiment, as shown in, comprises a permanent magnetand a magnetic field sensor arrangementwith a first magnetic field sensorand a second magnetic field sensor. The first magnetic field sensorand the second magnetic field sensorare formed by identical components, for example Hall-effect sensors. Each of the two magnetic field sensors,has five terminals: a supply terminal (Supply) and a ground terminal (GND), an output terminal (Output) and two test terminals (Test1 and Test2) which enable both input and output of signals. A three-dimensional Hall-effect sensor can for example be used as a magnetic field probe.

In the embodiment shown in, the input/output interfacecomprises only three terminals, namely the power supply terminal, the ground terminal, and the output terminal. The two magnetic field sensors,are, according to the arrangement shown in, wired up such that the first magnetic field sensoris configured as master, while the second magnetic field sensoris configured as slave. The measuring signals are transmitted from the output of the magnetic field sensorvia the communication bus, for example according to a SENT protocol, to the magnetic field sensoracting as master.

In the embodiment of, the masterevaluates the data of the slavestogether with the data of its own magnetic field probe, and thus a doubled measuring range, in comparison with that of an individual sensor, can be achieved. Further, the connections between the two magnetic field sensors,and to the input/output interface can take the form of a leadframe. If both magnetic field sensors,include integrated EMC/ESD protection circuits respectively, no PCB is required.

In another embodiment shown in, the master-slave arrangement shown inhas a mechanical solution. The two magnetic field sensors,are arranged such that their terminals face each other.

In another embodiment shown in, the first magnetic field sensorand the second magnetic field sensorare wired up to form a multimaster architecture. Each of the two magnetic field sensors,acts as both master and slave. As is evident in, both magnetic field sensors,perform a magnetic field measurement. The generated measuring signals are transmitted via the data bus linesto the respectively other magnetic field sensor. Each of the two magnetic field sensors,includes a calculating unit which calculates the position of the permanent magnetfrom the combination of the two measuring signals and generates a corresponding output signal. The input/output interfaceis constructed such that the actual position signal is output on the output terminal, while the output signal which is complementary thereto is located on the complementary output. In such an embodiment, an additional fault monitoring possibility is created by the obtained redundancy. A mutual signal evaluation can take place and thus a redundant output signal can be generated; the complementary output signal is redundant to the output signal.

, it should be noted, are not to scale and in particular do not reflect the relative dimensions of the permanent magnetand the individual magnetic field sensors, and the terminals and interfaces.

The mechanical implementation of a magnetic field sensor arrangementis shown in. The input/output interfaceis constructed as a so-called NanoMQS plug connector. Fixing devicesenable the magnetic field sensor arrangementto be fastened to a further component, for example with the help of a screw connection. The magnetic field sensor arrangementis advantageously hermetically protected in an electrically insulating housing. The housingencloses all the magnetic field sensors,for protecting the magnetic field sensor arrangementfrom outside influences, in order to prevent dirt, gases and moisture from entering.

A production of the magnetic field sensor arrangementwill be explained in detail hereinafter with reference to.

A production method for a magnetic field sensor arrangementaccording to the present invention begins with the provision of a leadframeshown in, which also illustrates a perspective view of an embodiment of a leadframeas described with reference to. The leadframeis produced from metal by stamping and bending, for example. In the shown embodiment, the leadframehas a three-dimensional shape and includes both the internal connecting lines and the terminals of the input/output interfacewhich are directed outwards. An additional reinforcing bracketensures greater mechanical stability. The conductor tracks, which are actually separate, are still connected to each other by connecting webs.also illustrates the connecting lines or lead linesthat are part of the busthat connect the first sensorand second sensor, as described with reference to.

In a next step, shown in, the leadframehas plastic injection molded around it such that a carrieris formed. The complete plug connector for the input/output interfaceand the fixing devicesare already formed on the carrier. Receptaclesenable the subsequent assembly of the magnetic field sensors,. The reinforcing bracketbinds a reinforcing ribto the plastic material surrounding it. After the leadframeis molded in, the connecting websare removed. The individual lines of the leadframeare thus electrically and mechanically separated from each other.

shows the carrierafter assembly of the magnetic field sensors,. The individual contacts of the magnetic field sensors,are welded to terminals of the leadframe, for example via laser welding. In other embodiments, other possibilities for the electrical connection, such as soldering, are of course also usable. The use of leadframesenables a geometrically precise alignment of the magnetic field sensors,with respect to each other and with respect to the fixing deviceswhich determine the position accuracy during later installation in the application environment.

To conclude the production process, as shown in, the sensor,is hermetically sealed with the help of a cover capwhich forms the housing. The mechanical connection between the carrierand the cover capcan take place, for example, via laser welding or ultrasonic welding. Other possibilities such as an adhesive bond are of course also usable.

schematically shows, in the form of a signal flowchart, the evaluation of the sensor architecture fromin the event that the first magnetic field sensorand the second magnetic field sensoreach have a 3D Hall probe as a magnetic field probe.

In a first step (S), each Hall probedetects the three components Bx, By and Bz of the magnetic field which is generated by the permanent magnet. In the following step S, a correction of the gain and the offset is carried out by each of the two magnetic field sensors,. In step S, the generated signal is transmitted to the respectively other magnetic field sensor for a fault diagnosis, and it is determined whether or not a fault is present (S). If no fault is detected or if the fault is based on the fact that precisely one of the two magnetic field sensors can no longer detect the magnet (steps Sand S), the two Hall-effect signals generated in step Sare combined in each of the magnetic field sensors,(step S) and the signal is linearized (S). Finally, the first magnetic field sensoroutputs the output signal in step S. By contrast, the second magnetic field sensorperforms an inversion of the signal (S) such that the complementary output signal is output by the second magnetic field sensor. These two redundant signals can be evaluated for fault monitoring.

The inventive combination of the signals of two Hall-effect sensors,, as is apparent in, generate an approximately linear signal across a larger position range. In, the curverepresents the output signal of the first magnetic field sensor, while the curveindicates the output signal of the second magnetic field sensor. By combining the two signalsand, the overall signalis obtained. This overall signalis calculated by the sum of the two individual signals divided by 2.

Connecting the magnetic field sensors,via the data buscombines a number of magnetic field sensors, which can be selected in a flexible manner where applicable, to form a highly integrated magnetic field sensor arrangement, without the necessity for a separate control and calculating unit, in order thus to cover an extended measuring range. The magnetic field sensor arrangementcan be adapted simply and at low cost to particular application requirements, in particular with respect to the path length which is to be detected. Due to the fact that each magnetic field sensor,includes all the components required for its operation and for complying with the EMC/ESD and electrical requirements, no further components are required, so the magnetic field sensor arrangementaccording to the invention has no need of a printed circuit board (PCB). The magnetic field sensor arrangementaccording to the invention is, in comparison with known sensor platforms, more reliable and more robust, needs fewer parts, costs less to produce, and takes up less overall space.